It’s a warm Indian summer day in San Francisco, but Michelle Richmond is wearing corduroy pants and a V-neck sweater. “It’s cold where I live,” she says, laughing. Her home is a mere seven miles away as the crow flies, but the difference in weather between the Outer Richmond and Noe Valley is vast.

The meeting is at Alice’s restaurant, one of many San Francisco locations mentioned in her latest book, “No One You Know.” In this book, as with her previous novel, 2007’s “The Year of Fog,” Richmond expertly captures the mood and the feel of the city she’s lived in for the past 10 years with her husband and young son.

Petite, with straight reddish hair and dimples you could slip a dime into, Richmond exudes happiness, which is somewhat surprising. Both books have dark sides: In “The Year of Fog,” the subject is a missing child; In “No One You Know,” the unexplained death of Lila, a brilliant young mathematician, haunts her sister 20 years later.

Richmond has to think for a moment to remember how she got the idea for “No One You Know.” “I knew I wanted a story to start in an unfamiliar place, with a weird encounter between two people. I knew it would involve a sister who had a sister who died 20 years ago. I wish I knew where it came from,” she says over garlic scallops.

Richmond says that as “The Year of Fog” was sort of panic-driven, she wanted a more patient book, where the tragedy occurred in the past. “I wanted to explore the reverberations. How does it shape your life?” she says. “I have two sisters. I’ve always been interested in that you can grow up with someone and then 20 years later realize you didn’t known them at all, only the basic facts of their lives.”

Appealingly alien

The author, who grew up in Mobile, Ala., says she’s always had a knee-jerk negative reaction to anything having to do with math, which makes it surprising that “No One You Know” has a character studying complex equations. The average math-hater probably would not go near the subject, but Richmond’s impulse is to dive right in.

“I thought it’d be fun to delve into something I knew nothing about,” she says. “I had brain jam a couple of times. It was like I was back in high school doing algebra; it was totally opaque. I couldn’t get past the surface of it.”

Richmond says she always likes to have something in her books that she doesn’t understand because she tends to find metaphors inside the research. In “No One You Know,” it was the idea that math is absolute. “So, I really just kind of like the idea of a whole family who never had any proof that was absolute. They just sort of accepted the story (written by a true-crime writer).”

Tough decisions

The identity of the person responsible for Lila’s death was unknown to Richmond until she was halfway through writing the book. She toyed with the idea of the killer being Thorpe, who wrote the true crime novel about the case, but her editor guessed it right off the bat, so Richmond decided it was too obvious. Then she thought about it being the wife of Lila’s lover, Peter, but she didn’t want it to be a woman scorned. “I knew it wouldn’t be Peter because I liked the idea of this person whose life had been ruined by a false story.”

Some of Richmond’s inspiration comes from Eastern European literature, which her husband, whom she met in an MFA program, turned her on to years ago. “It’s hard to explain; it’s more of a feeling in a story. The absurd always seems to be lurking in the background.”

Although her husband is now an FBI agent, he is still always Richmond’s first reader and editor. The couple discusses the stories before she writes them. “He’s very nice, but direct,” she says. “I write every word, but I do think they would be different books if I didn’t have his voice in the background.”

Richmond’s next book is due to the editors in December, and she hopes it comes out next year. She doesn’t want to say too much, but says it takes place in 2010, in a time of political upheaval, and readers are sure to recognize many characters. And yes — for those who love the city as much as Richmond does, they’ll be pleased to know it takes place in San Francisco.